Efforts have been devoted to characterizing the function of mitochondria in Trypanosoma brucei and related trypanosomatids. Major efforts have been made to identify the functional oxidases in these organisms. Bloodstream forms of African trypanosomes lack functional cytochromes in their mitochondria. Instead, they have present in extramitochondrial bodies an L-alpha-glycerophosphate oxidase (alpha-GP oxidase) which reacts with O2 producing H20 and not H2O2. Neither pyridine nucleotide coenzymes nor cytochromes are present. An L-alpha-glycerophosphate dehydrogenase is a component of the system. This particulate alpha-GP oxidase system has been partially purified from Trypanosoma evansi by sucrose density gradient centrifugation and its oxygen kinetics investigated. The alpha-GP oxidase bodies banded at a density of 1.16 gm/ml. In the presence of alpha-GP and BSA, the oxidase has a Km equals 2.1 plus or minus 0.4 micron M O2. In the absence of BSA, the oxidase activity and Km are decreased 4-6 fold. The reciprocal plots in the presence and absence of BSA are parallel. The enzyme is inhibited only slightly by CO and it is not inhibited by KCN or azide. However, it is inhibited by salicylhydroxamic acid (SHAM) and the trypanocidal drug, suramin. SHAM inhibits by reacting irreversibly with the oxidized form of the alpha-GP oxidase. The oxidases present in culture forms of T. brucei include primarily cytochrome aa3 and an azide and SHAM insensitive oxidase, probably cytochrome o. These oxidases have a very high affinity for oxygen, the apparent Km equals 0.12 plus or minus 0.04 micron M O2. BIBLIOGRAPHIC REFERENCES; Hill, G.C. and Pettigrew, G.W. 1975. The amino acid sequence of Crithidia fasciculata cytochrome c 555. European Journal of Biochemistry 57: 265-271. Hill, G.C. 1976. Electron transport systems in Kinetoplastida. Biochimica et Biophysica Acta. Accepted - in press.